Heretofore, there has been proposed an engine control device for an internal combustion engine with an automatic transmission which is adapted to prevent the engine speed from decreasing by increasing intake air through control of an idle speed control valve, causing the valve to open when load is applied to the engine due to a shift of the automatic transmission from its neutral range to its drive range. Such an engine control device is known from, for example, Japanese Unexamined Patent Published No. 61(1986)-279751.
In the engine control device described in the above publication, fuel is increased depending upon an compensatory increase of intake air caused by the idle speed control valve and detected by an airflow meter. However, it has a problem in that the air to fuel ratio of the fuel mixture tends to become lean and that, accordingly, a drop in engine speed cannot be prevented effectively. This results from the late detection of an increase in intake air quantity caused due to a volumetric capacity between the engine and airflow meter which attributes to the delay of supplying fuel.